This prospective study was conducted in the 25-bed medical intensive care unit of a university hospital. The goal of our study, conducted in critically ill patients with acute circulatory failure, was to test if PI changes could accurately detect a positive response of CI to a PLR test. In this context, monitoring PI might be an attractive method for assessing the effects of the PLR test when no direct measurement of CI is available. Then, the changes in the ratio of pulsatile over non-pulsatile component of the plethysmographic signal may depend on the changes in CI.
CMH CONSTRUCTOR STUDENT FREE SKIN
Some plethysmographic devices like the Radical-7 (Masimo Corp., Irvine, CA, USA) automatically calculate the ratio of the pulsatile over the non-pulsatile component of the plethysmographic signal, which is called PI and reflects the quality of skin perfusion. The pulsatile component reflects changes in the finger blood volume during one cardiac cycle, which may depend on the changes in stroke volume, while the non-pulsatile component is related to the light absorbed by the other tissues, such as connective tissue, bone, venous and capillary blood. The plethysmographic signal has two components. The peripheral perfusion index (PI) is derived from the plethysmographic signal of pulse oximetry, which is obtained from the amount of infrared (940 nm) light transmitted through the vascular bed of a finger. Nevertheless, to detect the changes in CI induced by a PLR test, a direct and real-time measurement of CI is needed, which is often invasive. The test has been demonstrated to be reliable by many studies and two meta-analyses.
It increases the mean systemic pressure, resulting in an increase in the pressure gradient of venous return and in CI in preload responsive patients. The PLR test induces the transfer of some venous blood from the lower part of the body toward the cardiac cavities. It consists of moving the patient from the semi-recumbent position to a position in which the trunk is horizontal and the inferior limbs are passively elevated at 45°. The passive leg raising (PLR) test is one of the methods currently available for this purpose. If preload responsiveness is not obvious, as in the case of fluid loss or at the initial phase of septic shock, it is crucial to predict the response of cardiac output to fluid administration before performing it. Moreover, excessive fluid loading with positive cumulative fluid balance may have deleterious effects and impair prognosis of critically ill patients, especially in cases of septic shock and acute respiratory distress syndrome. However, increasing cardiac preload with fluid administration does not always induce the increase in CI that was expected from it. Volume expansion is often the first-line treatment used to increase cardiac index (CI) in patients with acute circulatory failure.
0 kommentar(er)
